The present invention generally relates to a power supply system for corded/cordless power operated devices, and more particularly to a power supply system for an AC/DC power tool that automatically switches from battery power to corded DC power without having to remove the battery pack from the power tool.
Hand-held power tools equipped both with a battery pack and a corded DC power pack (e.g., an AC to DC power converter) are well known. The battery pack allows the operator to utilize the tool in places where AC power might not be available, or where the cord from a corded DC power pack might hinder the operator from using the tool effectively, for example. The corded DC power pack, on the other hand, allows the operator to use the tool when the charge on the battery pack is low or has depleted. When that happens, the depleted battery pack would be detached from the tool and the corded DC power pack attached in its place.
A problem associated with the conventional battery/corded DC power system is that the battery pack must be removed before the corded DC power pack can be used. In addition to being an inconvenience, the battery pack can become lost when separated from the tool. Further, in the battery/corded DC power system, a separate battery charger is typically required to charge the battery pack. A battery charger may or may not be provided by the manufacturer of the power tool. In any case, the operator generally bears the cost of the battery charger.
Accordingly, it is a primary objective of the present invention to provide an improved power supply system for an AC/DC power tool.
Another object of the present invention is to provide an improved power supply system which is adapted to switch from battery power to corded DC power without having to remove the battery pack from the power tool.
Yet another object of the present invention is to provide such an improved power supply system which automatically charges the battery pack while supplying power to the tool.
Still another object of the present invention is to provide such an improved power supply system having a switch which electrically disconnects the battery pack from the power tool an instant the corded DC power pack is connected to the power tool.
A further object of the present invention is to provide such an improved power supply system which prevents an over-voltage condition on and damaging the battery pack.